This invention relates to gas chromatography, and more particularly to a method and apparatus for introducing liquid samples into the carrier gas stream of a gas chromatograph.
Heretofore, sampling was effected by means of a hypodermic syringe, but the use of such a syringe involved some important disadvantages, as follows: (1) In spite of the fact that the sample was instantaneously injected, low-boiling point components vaporized more rapidly in the heated sampling system than the high-boiling point components. Therefore, withdrawal of part of the sample vapor for analytical purposes resulted in the sampling of a component mixture, whose component mixture ratios differed from those of the original sample. (2) The use of a syringe required a skilled operator. (3) Routine application of this syringe sampling method resulted in leakage of the injection membrane. (4) Inaccurate sampling quantities were introduced into the column. (5) The method was not very suitable for automated sampling injection.
In an attempt to overcome the foregoing problems, the patentee of U.S. Pat. No. 3,668,834 proposed a method of injecting a sample into a chromatographic column by passing a continuous stream of carrier gas through the column, passing a separate stream of a gas or liquid to be sampled, and diverting part of the separate stream into the carrier gas stream through an unrestricted sample injection limb, by varying the pressure difference across the limb. The present invention is an improvement over such prior art systems, as will become apparent as the description proceeds.